U.S. Secretary of State Hillary Clinton on Thursday urged Syrian President Bashar al-Assad to transfer power and leave his country.

Clinton make the statement at a joint press conference with Turkish Foreign Minister Ahmet Davutoglu on the sideline of the two-day Global Counterterrorism Forum in Istanbul.

Violence in Syria is "simply unconscionable," Clinton said, blaming Assad for the killings.

She said the United States will continue to mount political and economic pressure on the Syrian government. "We will intensify our efforts to support the Syrian people given the urgency of the situation," she said.

Clinton said foreign ministers from several Western and Arab countries held an unofficial meeting in Istanbul Wednesday night and discussed additional steps on Syria, including further support for the Syrian people and coordination on an effective and credible transition process that led to "a inclusive and democratic post-Assad Syria."

"We discussed a number of steps that we intend to take together, " she said, proposing three principles, including that Syrian government must implement all of the six-point Annan initiative, Assad must transfer power, and an interim and representative government must be established through negotiations.

"We are firm in our principle and we believe that we have to keep faith and do justice to desperation of the Syrian people," she added.